Electron beam convergence systems



March 6, 1956 E ERELLY "Fr AL W A55-'$737,509

I ELECTRON BEAM CONVERGENCE SYSTEMS Filed Nov. 50, 1950 2 Sheets-Sheet 1 NQ w mw w HT Nw my un @Mmmm mwmw S S S @LV "QHHL- G. E. KELLY ET AL 2,737,609

ELECTRON BEAM CONVERGENCE SYSTEMS March 6, 1956 2 Sheets-Sheet 2 Filed NOV. 30,' 1950 w 0, y W/ i www wu 4 fkz Nw V .F

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United States Patent 'i0 ELECTRON BEAiVI CONVERGENCE SYSTEMS Gordon E. Kelly, Collingswood, and Robert D. I lood, Haddonield, N. J., assignors to Radio Corporation of America, a corporation of Delaware Application November 30, 1950, Serial No. 198,314 15 Claims. (Cl. S15-4 3) This invention relates to systems `for controlling the electron `beams o f cathode ray tubes. It pertains particularly to the control of a plurality of electron lbeam com ponents used in a cathode ray tube so as to effect convergence of said components at all points of a raster scanned in a predetermined plane.

The problem of controlling the convergence of a plurality of electron beam components as they are dellected to scan a raster at a target electrode, for example, one lying ina predetermined plane is one which is 4frequently encountered in present-day practice. In television systems, for example, the trend is `toward the use `of kinescopes having target electrodes in Ythe form ofluininescent screens which are iiatter and of greater area `than heretofore used. Also, the overall length of such tubes tends to .become shorter. The problem of deflecting ,an electron beam, Or a plurality 4of electron` beam components, .in tubes of this character requires the use of techniques for effecting convergence of the electron beam components at all points in the raster plane which heretofore lhavenot been required.

A particular example of such a cathode raytube, which will be referred to herein for illustrative rather than restrictive purposes, is a multi-color kinescope for .use in` color television systems. A representative multi-color kinecope forms the subject matter of a United States Patent No. 2,595,548 of Alfred C. Schroeder, granted May 6, 1952. This tube has a luminescent screen consisting of a multiplicity of phosphor areas of-.sublemental dimensions. The rdifferent phosphorareasrarecapable of producing a light of diiierent colors when `excited electron beam energy. The different screen 4.areas are scanned by a plurality ofelectron beams, .from separate guns, which approach the screen from diiferent angles through an apertured masking electrode. 4Color yselccjii-on is ,eiected by the `angle of electron `beam,approach tothe screen.

Another multi-color kinescope of the typeadapted to employ the present invention forms the subject matter of a copending'United States applicationof iRussell R. Law, Serial No. 165,552, `tiled June l, 1950,.and titled `Color Television." In most respects, the tube lof .the typeproposed by `Law is essentiallysimilar to the tube .proposed by Schroeder; the chief difference is that the Law utype of tube employs a single electron gun lto produethe plurality ofelectron beam components. This is Y`eiected by imparting a ,spinning typetof movement tto the l:beam so-,that it is caused to'rotate about the central orlo gitudinal axis of the tube. In rotating about the ktube axis?, itoccupies, at successive intervals, substantially the saine positions asthose occupied bythe separaterelectronbearns of the Schroeder tube. n

The expresion electron bearncomponents, as` used in this specilication and claims, is intended to,cover`the type ofrphosphor-exciting electronic energy yp roducedby a singleor a plurality of electronguns. This energyrnay s ystemifor controlling the operationofra cathodefra'y tube,

' multiecolor.kinescopesr be continuous or pulsating asreqniredwithout departing from the scope of the invention.

ICC

I n order to successively operate a multi-color kinescppe of the type referred to, it is necessary that the plurality of electron beam components be made to converge substantially in the plane of the masking electrode at ail points in the scanned raster. Since the different points of the raster scanned in the plane of the target electrode are at different distances from the point of electronbeani deection, it is seen that it is necessary .to provide dynamic convergence control of the electron beain corn; p'onents in order that they may bemade to converge in the desired manner. n

One such electron beam control system forms .the suhject matter of a copending United States application of ,Albert W. friend, Serial No. ,1.6.4,444a11er1 May ze .1.950. and titled Electron Beam Controlling Systenlf H la the Friend application, there ,is provided an electron- ,Opticail .System which is variably .energized .as funs" af both the horizontal and vertical deection frequeni :s at

which the electron beam components are wdeiiected.: demonstrated inthe Friend application, it is seen that `v`the dynami agnvergence Control, both at horizontal lamt-veri s vapproxiignately parabolic in form.

.a Parabolic ,wave form. particularly at theh'o deectiqn frequency, for dynamic sQaveraence cf ,la Phirality Qfkelectren beam components, Yatecillir`es` the` useuf relatively complex and expensive apparatus.' 4'This.r,.es r1.1lf$ from 4the character of the wave and -the requiementsof the system. v The magnitude of the wave `used forfeiecting convergence must increase with increases in the angle of deflection from the central axis of lthe tube.` Accordingly, at `the corners and edges of `thescauned raster, fthe total peak-,to-peak voltage of the parabolic'wavefinujst he exceedingly high. Accordingly, it is an object of the .present invention to provide an `improved electron beam control systen ,by which to eiect convergence of `a plurality `,of electron beanrcomponents substantially at allfp'oints in .theltpl Ie of `a ,target electrode Withoutthe necessity Vof gener," complex `Wave forms. Y Y 7 n Another object of the invention is to ,provide ,an irnproved `beam `control system for a multicolordtinescpe in which convergence 1of a .plurality .of `electron .beam cqmppnents is `eiected under the control of energy y,ing substantially asinusoidal wave form. u i i i Still Ianother object of the invention is to pronide. ,an improved electron beam convergence control "system ,in which substantially .n sinusoidal control `fwave ,forms-arte derived ,frmne aonsiniply developed `from energy zontaldeiiection wave generators. p f l ,A further object of .the invention is to provvide, .in a

an improvedlgenerator of electrical control waves. j

The invention is employed in `conjunction an electron-optical system `for effecting convergence of Aa plurality ot electron ;beam 4 components substantially at all ,points `of a target `electrode of `theltypea.ernbodiedin The,Cathodezrayvtubesprydsd with a field-producing rneans located adjacent Ato thepaths of the ,electron lbeam components. The-eld-producing means .is energized, `first, as a parabolic fnnctignagtlie Yertical `,beam deflection frequency,,and, second, .A a sinusoidal ,function vat the Ahorizontal .beam detiection frequency- Y More '.speciically, in accordance with anjernbpdirnent of the invention in conjunction withmamulti color scope wherein the electron beam Vc rnnponents are den d, respectively, from different electron guns, thetield-pro'- ducing means includes anodes of the kinescope. The parabolic wave at vertical beam deection frequency is produced by integrating a saw-tooth wave derived from the vertical deection wave generator. The substantially sinusoidal convergence control Wave at horizontal detiection frequency is produced by exciting a parallel tuned circuit, resonant at the horizontal deflection frequency, by means of a parabolic wave at this frequency derived from a point in the horizontal deflection wave generator.

The novel features that are considered characteristic of this invention are set forth with particularity in the appended claims. The invention itself, however, both as to itsorganization .and method of operation, as well as additional objects and advantages thereof, will best be understood from the following description when read in connectionfwith the accompanying drawings.

"In'the drawingsz Figure 1 is aA block diagram of a television receiver embodying the present invention; Y Figure 2' is a graphical representation of the manner in which the system embodying the invention operates; Figure 3 is a fragmentary schematic diagram of an illustrativeform of a horizontal convergence controlwave generator in accordance with the invention; and, i V f'l-Tigur'e 4is another fragmentary schematic diagram of anillustrative embodiment of a vertical convergence control, way,e. generator in accordance with this invention. g `Reference rst Iwill be made to Figure l for a description of the general formof a television receiver in which Athe present invention may be embodied. The receiver includesan antenna 11'to which is coupled a conventional television signal receiver 12. It will be understood that thfej receiver 12 may include such conventional apparatus as carrier wave ampliers, a frequency converter and a 4'carrier wave demodulator or signal detector. Accordingly, the video and synchronizing signals will be underfstood to be derived from the receiver 12. The video signals are'impressed upon a video signal channel 13 and the synchronizing signals are impressed upon a synchronizing signal separator 14. The video signal channel 13 isv coupled to the electron beam control apparatus of an image-reproducing device, such as a kinescope 15. A* jIn the present instance, it is assumed that the invention is embodied in a color television system. In this case, the kinescope 15 may be of either of the types disclosed in theSchroeder patent and Law application previously referred to'.- For illustrative purposes, it is assumedv that the kinescope 15 is of the general type disclosed in the Schroeder patent. The luminescent screen16 of the kinescope 15 consists of a transparent flat platev which is mounted inback of, and somewhat spaced from, the end wall 17 of the tube. The luminescent portion of the screen, which is on vthe side of the` transparent plate remote from the end-wall 17, consists of a multiplicity of groups of phosphor'elementsLeach element being of such size that a group v,of them is'of elemental image dimensions. For example, one such group of phosphor elements or d ots consist o f the red, green, and blue light-producing dots 18, 19fand 20, respectively. The' groups -of phosphor dots may be larranged in any desired pattern, such as clusters of circular, triangular, hexangular or other configurations, oneven in linearfstrips extending from one side of the screen'to the other.

For use in conjunction with a luminescent screen of thepcharacfter described, the tube 15 also is provided with anapertured masking electrode 21. This electrode is mounted in back of, and in spaced relation to, the screen 16."= It* also is provided with apertures, conforming in shape substantiallyto the configurations of the groups of rSljl'nsplior'dots.A For example, in the case of substantially circulr'giroups kof phosphor dots, the apertures Isuchas 22 will `be substantially circular. One aperture is provided in this' electrode for each group of phosphor dots; The

pertures'vof'the masking electrode 21 also are arranged withre'spect-to the associated groups of phosphor dots 4 so that proper selective excitation of the phosphor areas may be effected'to produce the desired component colors of the image.

The multi-color kinescope 15, also in accordance with the disclosure of the Schroeder patent referred to above, is provided with three electron guns 23, 24 and 25, which will be referred to hereinafter as the red, green and blue guns, respectively. These designations are made because the electron guns are effective to excite the red, green and blue light-producing phosphor areas of the screen 16. Also, as part of the electron-optical system of the tube, there are provided with, or as part of the electron guns, second anodes 26, 27 and 28. These anodes serve to focus the electron beams produced respectively by the guns 23, 24 and 25 into the target area which includes the screen 16 and the masking electrode 21. Such electronoptical apparatus will be understood to be conventional in substantially any cathode ray tube.

AThe kinescope 15, however, in the present instance, includes an additional electrode 29 having a substantially cylindrical form for use in effecting convergence of the three electron beams in the plane of the masking electrode 21. This is indicated schematically in this figure of the drawing. For example, in order to excite the red,- green and blue light-producing phosphor dots 18, 19 and 20, respectively, the electron beams indicated at 31, 32 and 33 converge in the aperture 22 of the masking electrode 21 substantially as shown. Travel of the electron beams beyond the masking electrode causes impingernent With the proper phosphor dots or luminescent screen.

The individual electron beam-focusing electrodes 26, 27 and 28 function by reason of having impressed thereon a'potential of the order of 3,000 volts which is of positive polarity relative to the cathodes of the electron guns 23, 24 and 25. The convergence anode 29 functions in conjunction with the conventional electrode structure of the kinescope 15 to produce a field' by which to effect the desired convergence of the electron beam. This field is produced by impressing a potential upon the'convergence anode 29 of the order of 6,000 to 7,000 volts relative to the focusing anodes 26, 27 and 28.

The mannerV in which these potentials are applied to the electron-optical system of the kinescope 15 as described, is indicated diagrammatically. vA source of unidirectional voltage, such as indicated by a lbattery 34, has connected to the terminals thereof, a voltage dividing resistor 35. The negative terminal of ther power supply 34 is grounded and itis assumed that the cathodes of the electron guns 23, 24 and 25 are operated substantially at ground potential. The focusing anodes 26, 27 and 28 are shown connected to a relatively low positive voltage point on the voltage divider 35'. In a similar manner, the con- Y vergence electrode 29'is shown connected to a more positive point on the voltage divider 35 by a circuit which includesa relatively high impedance resistor 36. For further information regarding the operation ofv beam convergence apparatus with which the present invention may be employed, reference may be had to a publication dated April 1950 by Radio Corporation of America and titled General Description of Receivers for the RCA Color Television System Which Employ the RCA Direct-View,

Tri-Color Kiuescope.

The kinescope 15 also is provided with a beam-deflecting Isystem which, in the present case, includes an electromagnetic yoke 37. The deectingyoke is mounted in the usual manner around the outside of the neck portion of the kinescope adjacent to the conical section thereof. It also is energized in a conventional manner, which will be referred to subsequently.

The synchronizing signal separator 14 is coupled to horizontal and vertical deflection wave generators 38 and 39, respectively. These generators may be entirely conventional. Accordingly, it will be understood that a substantially saw-tooth-wave,such as 41 at the line scanningfrequency, is derived from the horizontal deflectionvwave 5 generator 38 vand ,is impressed upon the yoke 3,7. Similarly, a substantially saw-tooth wave, Vsuch as 42 at the field `scanning frequency, is derived from the vertical delection wave generator 39, and also is impressed upon the `yoke 37.

The system, in accordance with the present invention, also includes horizontal and vertical convergence control wave generators 43 and 44, respectively. The input circuits of these .generators are coupled to the horizontal and vertical deflection wave generators 38 and 39, respectively. The output circuits of `the convergence control wave generators are combined with one another and are coupled by a capacitor 45 to the convergence electrode 29 of the kinescope 15. By such an arrangement, there is impressed upon `the convergence electrode 29, a dynamic control `wave, in addition to the steady energization Athereof previously described. The junction point between the output circuits of the generators 43 and 44 is by-passed to ground by a capacitor 46. This capacitor provides a by-pass for the horizontal control wave and, at the same time, provides a high impedance for the vertical control wave.

In this form of the invention the horizontal convergence control wave generator 43 has its input circuit connected to a point in the circuit of the horizontal deflection wave generator 39 from which there may be derived a wave such as 47 having a substantially parabolic form and a frequency corresponding to the line scanningfrequency. One convenient point in the horizontal deflection wave generator 38, from Which the parabolic wave 47 may be derived, vis the damper-booster apparatus. A typical damper-booster of the type referred .to is disclosed in an article by Albert W. Friend titled Television deflection circuits, published at page 9S of the March 1947 RCA `Re view, volume VIH, No. l. A representative form of such a damper-booster is shown in Figure 19 of the article.

Another convenient source of a horizontal frequency parabolic wave is the cathode ofthe horizontal deflection tube. The cathode circuit of such a tube usually includes a network which functions to integrate the current of sawtooth .form traversing it so as to produce a parabolic wave suitable for use in the practice of this invention.

The horizontal convergence control wave generator 43 functions in a manner to be described in greater detail subsequently to convert the parabolic wave 47 into a substantially sinusoidal wave, such as 48.

The vertical convergence control wave generator 44 may have its input circuit coupled directly to the output circuit of the vertical dellection generator 39. By this means, .a substantially saw-tooth wave, ,such as 42, is impressedupon the convergence control wave generator .44. This l.apparatus functions in a. manner to be described presently ,to1convert the saw-tooth wave 42 into a parabolic wave, such as 49. Y

The inter-coupling of the .output circuits ,of the yhorizontal and vertical convergence control wave generators 43 and `44 serves to combine the sinusoidal and parabolic waves.48land 49 for impression upon the convergence control electrode 29. The dynamic energization of this electrode by means of thesewaves effects convergence ofthe electron beams 31, 32 and 33 substantially-in the plane of the masking electrode 21 for all points in the raster scanned by deilecting these beams in `a conventional manner.

Before considering in more detail the vapparatus embodying the present invention, reference will be made to Figure 2. The purpose of thisiigureis `to illustrate graphically, `the general manner in which a sinusoidal wave may beused to effect dynamic convergence at the line `scanning frequency with substantially the same effectiveness asa parabolic wave. Inthis ligure, a portion of a repre-A sentative composite television signal wave is shown `by the curve 5l. The portion 52 represents `the `video `signal in one ,horizontalline of the image. The waveportions 53 represent the horizontal "blanking Vpulses and `the porsubstantially 6 tions -54 represent the ,horizontal synchronizing pulses. The horizontal blanking periods are indicatedas extend,- ing'from the leading to the trailing edgesv of the pulses 5 3,. Also, the horizontal line period is indicated as `extending .between the `trailing edges of `successive horizontal syn.- chronizing pulses 54. The picture period of veach horizontal line is indicated as extending between the trailing edge of `one of the horizontal blanking pulses 53 to the leading edge of the succeeding horizontal blanking pulse.

It will be understood that, since :the luminescent screen of the kinescope is notenergized by electron beamenergy during the blanking periods, attention need only `be given to `convergence of the beam component during the picture periods. It has been .determined that, with a minimum dynamic energization of the convergence electrode when the electron beams of the kinescope are directed 4toward the central point of the scanned raster, a maximum energization of this electrode is required when the electron beams are deflected toward the vertical edges of the scanned raster. The variation of this voltage should follow substantially a parabolic function.

Accordingly, in Figure 2, the Vbroken line curve `55 Vrepresents a voltage having a substantially parabolic form and a frequency equal to the horizontal scanning frequency. lt is seen that the positive, or upwardly extending, peaks of this wave coincide with the midpoints of the blanking periods between `horizrmtal lines. Also, it is seen that the negativepeaks of the wave 55 occurs substantially at the center of the horizontal lines. As graphically illustrated, a voltage variation represented by e is required to effect the desired dynamic beam convergence control in a horizontal sense. However, in order to develop a voltage having a substantially parabolic wave form for use in a system of this character, 'it is necessary to develop a parabolic voltage wave having vpeak-to-peak. ,amplituderrepresented by E Itis seen that a substantial portion of the total available amplitude of such a wave is not required in a system of this character. Approximately that portion of the voltage `represented by E, which exceeds the required voltage indicated by 12, is not needed.

Furthermore, in order to develop a parabolic voltage of the proper phase required, it isnecessary to employ an output transformer -having the capability of passing harmonies of the third order and higher with negligible .phase distortion. Such a transformer necessarily is an expensive component. It is seen, therefore, that an output tube having a higher power handling capability than is needed for the energization of the convergence electrode is required when parabolic -voltagewaves are employed and also an excessively expensive output transformer `must be supplied.

By'reference to Figure 2, it will be seen thata sinusoidal voltage `wave such as represented by the curve 56 may be employed in accordance with this invention `with substantially the same success as the theoretically required parabolic voltage ways. It may be `seen from an inspection of the curves 5S and 56 that, during mostof the picture period, the two waves closely coincide. The departure of the sinusoidal wave 56 from coincidence with the parabolic wave 55, occurs substantially entirely within the 4blanking periods between horizontal picture lines. Furthermore, it may be seen that the peak-to-peakamplitude of the sinusoidal Wave `56 is substantially equal to that required for the dynamic energization of the con-V vergence electrode as indicated by e.

lt will be understood by those skilled in .the art `that the use of a sinusoidal voltage wave 4for horizontal dynamic convergence control enables a material simplification in the design of the apparatus. Compared `with the problem of generating a parabolic Wave at thehorizontal deflection .frequency the generation of a sinusoidal wave of the same frequency `is quite simple. The power requirements are substantially less and also more economical components may be used. i

By referring 4now to Figure 3 of th'e "drawings, there 7 will be described apparatus embodying an illustrative form of the invention for derivation of the horizontal convergence control Wave having a sinusoidal form. The apparatus includes an electron tube 57 which, in the illustrated case, is a pentode, such as an RCA type 5763. The suppressor and screen grids of the tube are conventionally connected respectively to ground and to a source of positive potential relative to the cathode. The control grid of the tube 57 is connected to a potentiometer 58, upon the terminals of which is impressed a parabolic wave such as 47 by means of a capacitor 59 coupled to the horizontal deflection wave generator 38 as indicated. The capacitor 59 may be coupled to the cathode of the c VYoutput tube of Va conventional horizontal deflection waveY generator. It is customary to include in the cathode circuit of such a tube a network of resistance and capacitance of a character serving to integrate the substantially sawtooth current traversing the cathode circuit in a manner to develop a substantially parabolic voltage wave at the cathode.

The cathode of the tube 57 is connected to ground, or other point of fixed potential, by a resistor 61 which is by-passed for alternating currents by a capacitor 62. The anode of the tube 57 is connected to a source of positive voltage indicatedat +B through an inductance device such as a coil 63. Brietly, this coil should be of a character to permit a variation of its inductance for a purpose to'be described presently. Accordingly, it may be provided with a movable core if desired. The anode of thetube 57 is coupled by a capacitor 64 to the primary winding 65 of an output transformer 66. The transformer also is provided with a secondary winding 67 which is connected as indicated between the vertical convergence control wave generator 44 and the convergence anode 29 of the kinescope 15.

By means of the coil 63 in conjunction with the primary transformer Winding 65 and the capacitor 64, the output circuit of the tube 57 is tuned substantially to the horizontal' deection frequency of 15,750 cycles per second. By this means, there is `provided a sinusoidal wave output developed at the secondary transformer winding 67 of suicient magnitude to effect the desired horizontal dynamic -convergence control of the electron beam energy in the manner previously described. Phase control of the generated sinusoidal wave also may be effected by tuning of the coil 63. In this way the wave may be made to conform to the picture and blanking periods as described in conjunctionwith Figure 2.

The parabolic dynamic convergence control voltage at the field scanning-frequency may be developed in accordance with the present invention by means of apparatus such as that shown by Figure 4 to which reference now will be made. This'apparatus includes electron tubes 71 and 72 which may be triodes as illustrated. It will be understood that the two electron discharge paths may be combined within a single envelope in a double triode, such as an RCA type 12AU7. There is derived from the vertical dcection wave generator 39, a substantially saw-tooth voltage wave 42. This is impressed upon a network including a series resistor 73 and a shunt capacitor 74. By meansV of this network the voltage indicated at 42 is partially integrated and attenuated. Such a voltage then is impressed by a coupling capacitor 75 and resistor 76 upon the grid of the tube 71. The anode of the tube is connected to a source of positive voltage indicated at +B by load resistors 77 and 78. Accordingly, there is developed at the anode of the tube 71, an amplified wave similar to the input wave 42 but of oppositephase. A

similarvoltage is developed at the junction pointbetween the Vresistors 77 and 78.

' The cathode of the tube 71 is connected to ground, or other point of fixed potential, by serially-connected resistors 79 and 80. It will be noted that these resistors are unby-passed for alternating currents. Accordingly,

Vthere is4 developed by the resistors 79 and 80 a substan- The parabolic voltageY war/e158 is developed across the 8 tially saw-tooth voltage of the same phase as the voltage wave 42. The saw-tooth waves of opposite phase developed in the anode and cathode circuits of the tube 71 are combined with one another and also with a parabolic wave in a manner to be described for impression upon the tube 72.

There is coupled to the anode of the tube 71 an integrating network 81. This network consists of a series connection of resistors 82, 83 and 84 and a plurality of shunt capacitors 85, 86 and 87. By means of this network, the saw-tooth voltage developed at the tube 71 is integrated to provide a voltage such as indicated at 88 having a parabolic wave shape.

resistance portion of a potentiometer 89. The movable element of the potentiometer is connected by a coupling capacitor 91, and a leak resistor 92, therefor, to the control grid of the tube 72. The cathode of this tube is connected to ground through a resistor 73 which is bypassed for alternating currents by a capacitor 94. 'Space current for the tube 72 is derived from the power supply indicated at +B through a load resistor 95.

The other terminal of the resistor element of the potentiometer 89 is connected to the movable contact of another potentiometer 96. One terminal of the resistance portion of the potentiometer 96 is coupled by a capacitor 97 and a resistor 98 to the junction joint between the cathode-connected resistors 79 and 80 associated with the tube 71. The other terminal of the potentiometer 96 is coupled by a capacitor 99 to the junction point between the load resistors 77 and 78'associated with the anode of the tube 71. It is seen that, by means of these connections of the potentiometer 96, saw-toothV voltages of opposite phase are impressed upon the terminals of the potentiometer so that it may be used in a manner to be described presently.

The anode of the tube 72 is coupled` by a capacitor 101 Y to the primary winding 102 of an output transformer 103.

By such means the transformer is shunt fed from the load resistor and direct current saturation thereof is prevented. This transformer also has a secondary winding 104 which is coupled to the horizontal convergence control wave generator 43 as indicated and as shown speciically in Figure l.

The manner in which the vertical convergence control wave generator of Figure 4 operates is substantially as follows. As previously stated, the integrating network 81 functions to convert the saw-tooth voltage wave 42 into a parabolic wave 88. The magnitude of that portion of the parabolic voltage wave 88 which is impressed upon the grid of the tube is controlled by the ladjustment of the potentiometer 89. The connection of this potentiometer to the potentiometer 96 permits the addition of a saw-tooth voltage with the parabolic voltage.

By suitably adjusting the potentiometers 89 and 96 the Wave form of the output parabolic wave 49 may be controlled. A symmetrical parabolic wave 49 is generated by adjusting the potentiometer 89 so that a maximum amplitude ofthe parabolic wave 88 is impressed upon the control grid of the tube 72. If it is desired to make the output parabolic wave 49 unsymmetrical, the potentiorneter 89 is adjusted to impress a minimum amplitude of the parabolic wave 88 upon the tube 72. At the same time, an adjustment of the potentiometer 96 to one side or the other of its central position will distort the parabolic wave 49 in opposite senses depending upon the adjustment of the potentiometer 96.

For example, with the arm of the potentiometer. 96 moved toward that end of the resistor portion coupled tothe cathode of the tube 71, the output voltage wave has a form substantially as indicated at 49a. This is produced by the addition of a saw-tooth voltage of the phase developed at the cathode of the tube 71. An adjustment of the arm of the potentiometer96 toward the end of the resistor portion coupled to the vanode of the tube71 arcanos duces an opposite distortion of the parabolic output wave as indicated at 49b. It is "seen, therefore, that suitable manipulation of the potenticmeters 89 and 96 renders the apparatus susceptible of operating to control the amplitude of the parabolic output wave 49 and also to control its shape suitablyto enable the convergence electrode 29 `of the kinescope 15 to maintain beam convergence vertically throughout substantially the entire raster scanned by the beams.

It .may be seen from the foregoing disclosure of an illustrative embodiment of the invention that there is provided an improved system for effecting convergence of a plurality of electron beam components substantially at all points inthe plane of a target electrode without the necessity of generating complex wave forms. It is seen, from the demonstration made herein, that a sinusoidal wave so closely approximates the theoretically ideal parabolic wave during the .horizontal picture periods thata satisfactory result is obtained.

Furthermore, `such a sinusoidal wave has about the proper peak-to-peak amplitude to effect the desired convergence control. A sinusoidal wave is much easier to generate `than 'a parabolic wave. The apparatus used for such purpose, therefore, may be quite simple and inexpensive. Moreover, it is not necessary to4 generate a wave having a peak-to-peak amplitude which is greater than that necessary to -accomplish the desired result. In many cases, the ,peak-,to-peak amplitude of a ,parabolic wave is approximately 72% greater than that of a sinusoidal wave to accomplish substantially the same results. In addition, in order to develop a parabolic voltage wave of proper phase for use in a system of the character described, AVan output transformer is required which is capable of passing, in addition to the fundamental frequency, harmonics of the third and higher orders with negligible phase distortion. Such a transformer is a relatively `expensive component. Also, an output tube having 'a greater power handling capability is required when a parabolic'voltage wave is used as compared `with the tube necessary for use when a sinusoidal wave is employed.

Furthermore, it is seen that the illustrative .forms of the convergence control wave generators disclosed herein provide facilities 'for easily changing the phase of the control waves so as to obtain an optimum adjustment. Also, facilities are provided for suitably altering the shapes of some of the voltage waves .in order to `better adapt them Vfor use ina system of the character described.

The nature of the invention may be determined from the foregoing disclosure of an illustrative embodiment thereof. The scope of the invention is set forth in the following claims.

Whatis claimed is:

1. In a cathode ray tube image-reproducing system wherein nelectron beam energy is angularly deflected both horizontally and vertically relative to the longitudinal axis of the tube to scan a raster at aV target electrode, means for effecting said beam deflections under the control of waves having substantially sawtooth forms, a dynamic electron beam controlling system comprising, field-producing means disposed adjacent to the undeflected path of said electron beam energy, and means to produce a wave varying as a sinusoidal function of one o'f said beam deflections and having the same frequency as said one `beam deflection for energizing said lieldeproducing means. t

:2. In a cathode ray tube imagereproducing system wherein a plurality of electron beam components, effectively traversing paths spaced, respectively, about a longitudinal axis of the tube, are angularly deflected both horizontally Aand vertically .to scan 'a vraster ata target electrode, means for effecting said beam deflections under the control of waves having substantially sawtooth forms, a dynamic convergence system to effect substantial convergence of said beam components at all points in said raster comprising, field-producing means disposed ad- 10 jacent to the paths -of said beam components, `andmeans .to produce a wave varyingasa sinusoidalfunctionofone of Ysaid beam deflections and having :the same frequency as .said one beam deflection for energizing said fieldproducing means.

3. In a cathode ray tube image-reproducing system, the combination as delined in claim 2 wherein, said wavevproducing means includes a `circuit resonant at .substantially the `same .frequency as said one beamV deflection, and means to vary the tuning of said resonant circuit to effect phase control of said produced wave.

4. In a cathode ray tube image-reproducing system wherein a plurality of electron beam components, effectively traversing paths spaced, respectively, about a 1ongitudinal axis of .the tube, are `angularly deilected both horizontally and vertically .to scan a raster at `a tar-get electrode, means for effecting said beam deflections under ther control of waves having substantially .sawtooth forms, Aa dynamic convergence `system to effect substantial convergence of .said beam `components at .all points in said raster comprising, field-producingmeans disposed adjacent to the paths of said :beam components, and means to produce a Wave varying as a :sinusoidal function of said horizontal beam deflection, andvhaving said horizontal beam deflection lfrequency for energizing `said feld-producingmeans.

5,. .In .a cathode 'ray tube image-reproducing system wherein a plurality of electron beam components, effectively traversingpaths spaced, respectively, about a longitudinal Iaxis of the tube, .are angularly deflected .both .horizontally and vertically to scana raster at a target electrode, means for effecting said -beam deflections :under ,the control of waves .having substantially sawtooth forms, a dynamic convergence zsystcm to effect substantial convergence ofssaid .beamcomponents at .all points in .said raster comprising, field-producing means: disposed .adjacent to the paths `of said beam components, ,and means for energizing said field-producing means concurrentlytas functions of vsaid vertical and horizontal beam deilections, at least one of said functions :being sinusoidal, Vand Vsaid sinusoidal fenergization being at one of said beam deflection frequencies.

,6. In a cathode ray tube image-reproducing system wherein .a plurality-of electronbeam components, .effectively traversing paths spaced, respectively, about a Alongitudinal .axis `of the tube, vare angularly deflected both v.horizontally and lvertically to scan a raster ata target electrode, means .for eectingsaid beam deflections under the control of waves havingsubstantially sawtooth forms, -a dynamic Y convergence system to .effect .substantial convergence of said beam components at all points in said raster Vcomprising, fieldproducing Ameans disposed adjacent to the paths of vsaid beam components, .means to produce .a wave varying-as a parabolic functionvof `one 'of said beam deections for .energizing said field-producing means, and means Ato produce .a wave varying as asinusoidal function ofthe .other .of `isaid beamdeflections for additionally energizing .saidiield-producing means. Y

7. In a cathode ray tube image-reproducing system wherein a .plurality of electron beam components, .effectively traversing paths spaced, respectively, about a longitudina'l-axis of the tube, are angularly deflected both horizontally and vertically to scan arasterat a target electrode, means for effectingsaidbeam deflections under the'control of waves having substantially sawtooth forms, a dynamic convergence system to Aeffect 'substantial convergence of said '-beam components at all points in said raster com'- pris'ing, field-producing -means disposed adjacent vto `the pathsiofr-said beam components, means varying as a parabolic function tof fsa'id vertical '-beam dellection for Ienergizing said field-producing means, and means to produce a wave varying as a sinusoidal function of said horizontal beam deflection for additionally energizing said fieldproducing means.

8. Ina cathode ray tube image-reproducing system, the

combination as definedin claim 7 wherein, said -waveproducing means includes a circuitresonant atgsubstant'iallyv said horizontal beam deflection frequency, and means to vary the tuning of said resonant'circuit to effect phase control of said produced wave. f

9. In 'a vcathode ray tube image-reproducing. system wherein a plurality of Yelectron beam components, effectively traversing 'pat'hs spaced; respectively,vr about a longitudinal axis: of@4 the tube, A'are` angularly 'f deflected both 'horizontally'and vertically to scan araster-'in a predeterminedplane,adynarniciiconvergence system to effect i ,"isub'stant'ial convergence of said beam components at all points-'in'said ra'stercomprising, field-producing means disposed adjacent to the paths of saidv beam lcom'po i:ier its`,-

means varying asy a parabolic functio'nuof' saidfve'rtical beam deflection for energizing said'field-producingmeans,

a horizontal convergence control wave generator including an .electron tube havingl inputfand'output circuits, means -lfor impressing upon said vinput circuit a-'wave having a substantiallyA parabolic formand a frequency equal to the horizontal deflection frequency, meanstuning said output circuit to, said horizontal deflection frequency `whereby to h12 means for impressing upon saidv second tubeinput circuit a wave having a substantially parabolic formlan'd -affreL quency equal to the horizontal deflection frequency,`mea'ns' providing'parallel' tuningy of said-second -tube out'pnt cirl cuit at said 'horizontal deflection f'frefquen'cy, whereby' to' -levelopla.'wave having a-'subst'antially sinusoidal form?, f and means including output transformers coupled between y said `vertical and horizontal convergence control wavel generators respectively and said field-producing means for energizing said field-producing means 'concurrently as par-i` abolic and sinusoidal functions/respectively, off said ve'rtilv cal :and horizontal beam deflections.

12. Ina system for controlling the operation of a cath: oderay image-reproducing tube, an electrical fwave geni erator lcomprising first and second electron tubes, each Y- having input and output circuits, means impressing upon the Iinput circuit of said first tube a wave having a1sub f produce a-fsubstantially Asinusoidal wave at said horizontal deflection frequency, and means couplingsaid'horizontal control wave generator to said fleld-producingvmeans for additionally energizing said field-producing means as a sinusoidal function of said horizontal beam ,deflection k10.*In a cathode ray tube imagereproducing system wherein a plurality-of electron beam components, 'effectively traversing 'paths spaced, respectively, about a longil tudinal axis of vthe tube,- are angularly deflected ,both

horizontallyand verticallyto :scan a raster in avpredetermined plane, 'a dynamic convergence system to effect substantial convergence of said beam components at all points' insaid raster comprising, lfield-producing means' means including an inductance device coupled'to said output circuit forproviding p'aralleltuning of said output circuit at said horizontal deflection frequency, ,whereby to produce a substantially sinusoidal wave at said horizontal deflection frequency and means including a secondary winding of said transformer for impressing said sinusoidal wave upon said'feld-'producing means as a sinusoidal function of said horizontal beam deflection. i

1l. In a cathode ray tube image-reproducing system wherein a plurality of electron beam components, efectively traversing paths spaced, respectively, abouta longi- -tudinal axis of the tube, are angularly deflected both horizontally and vertically to scan a raster in a predetermined plane, a dynamic convergence systemvto effect substantial convergence of said beam components at all points lin saidraster comprising, field producing means disposed adjacent to the paths of said beam components,a vertical convergence control wave generator including a first electron tube having input and output circuits, lmeans for 'im-` pressing upon said first tube input circuit a wave having a substantially saw-tooth form and a frequency equal to' the vertical deflection frequency, integrating means in said first tube output circuit to produce a substantially parabolic wave at said vertical deflection frequency, a horizontal convergence control wave generator including a second electron tube having input and output circuits,

stantially saw-tooth form and a relatively low frequency, an integrating network coupled to the output circuit of said first tube and serving to convert said sawtooth fwave into a wave having a substantially parabolic'forrn land said relatively low frequency, means coupling said inte- Y grating network and the input circuit of said second tube for impressing said parabolic waveupon said second tube,- and means coupled to the output circuit ofsaid second tube for developing a wave having a substantially paral bolic form of the desired shape and amplitude.

13. An electrical wave generator as defined in claim 121 wherein, said means for coupling said integrating network to said second tube includes a first potentiometer, whereby to control the amplitude of the parabolic wave impressed upon said second tube.

14. An electrical wave generator as defined -in claim 13 having in addition, means coupled to the outputfcircuit of saidl first tube for developing a substantially sawtooth wave at 'said relatively low frequency, and means coupling said s'awtooth wave-developing means to the input circuit of said second tube, whereby to combine said sawtooth andparabolic waves in the output circuit of Vsaid second tube. n

' 1-5. An electrical wave generator as defined in claim 14 wherein, said sawtooth wavedeveloping means includes a second potentiometer coupled between two points ofA opposite phase in the output circuit of said first tube, said lsecond potentiometer being connected to said* first potentiometer and being adjustable to alter the phase of the' sawtoothl wave to be combined with said parabolic wave References Cited inthe ille of patent UNITED STATES PATENTS 2,178,093 Zworykin et al -'Oct. 3l, 2,220,303 Tingley Nov. 5, 1940 2,225,455 Klauer Dec. 17, 1940: 2,312,054 Schade Feb. 23, 19.43r- `2,312,761 Hershberger Manz, 1943' 2,338,646 Kessler Jan. 4,V r1944- 2,485,620 McCoppin Oct. 25, 1949 2,513,954 Moe July 4, 1950 2,514,079 Lockhart July 4, 1950- 2,518,200 Sziklai et al. Aug. 8, 1950 2,572,858 Harrison o 1951:V 2,582,271` f Page Ian. 15, 1952 2,584,9324 Snyder et al. Feb.- v5, 1952,` 2,594,513 Stocker Apr. 29, 1952#V 2,642,525 Horn et al. Iunel, 1953 2,687,493 Kirkwood Aug. 24, 1954' Y. FOREIGN PATENTS 866,065 France Mar.` 3l, 1941 

